When the frequency of an electromagnetic wave increases to the point where its wavelength becomes small compared to the length of the conductor carrying it the wave tends to radiate into free space. This radiation is prevented when the conductor is surrounded by a grounded electrical conductor as in the case of coaxial cable. The smallest commercially available coaxial cable to date is about 80 mils in diameter, which is large when compared to the environment in which it might be used. Areas which could utilize coaxial cable of a few mils in diameter are integrated circuit technology, shock wave measurements, biological uses, lightweight coaxial cables for satellites, spacecraft plasms probes for laser welders, and "invisible" cabling for home and institutional video products such as cable TV. In integrated circuit technology, a need to communicate between many high frequency chips can be favorably accomplished utilizing microminiature coaxial cable. In shock wave measurements, experiments on shock and detonation waves require the use of coaxial cable for velocity measurement. The coaxial cable must be very small in order to minimize its effect on the wave front. Since it is desirable to make the explosive experiment as small as possible, very small coaxial cable is desirable. In biological uses, microwaves in the human body and animals are becoming a regular research area. In particular, the local heating of tissue by microwave has been used in the treatment of cancer. To minimize the trauma of the conductor to the surrounding tissue, very small coaxial cable is desirable.
In order to be practical, a microminiature coaxial cable must also have low loss. The largest loss of energy is a resistive loss of the internal conductor. As frequency goes up, the skin effect confines the radio frequency signal to the surface of the center conductor, which in a normal coaxial cable center conductor is the circumference of a thin wire. If one merely scaled down normal coaxial geometry, the circumference of the center conductor would soon become too small to carry the signal without unreasonable loss. This problem is overcome by the preferred embodiment of the invention.
One object of the invention is to inexpensively manufacture microminiature coaxial cable.
One advantage of the instant invention is that the microminiature coaxial cable thereof can be utilized in many applications requiring coaxial cable of very small diameter.
Another advantage of the instant invention is that low loss is achieved in a microminiature coaxial cable.
Another advantage is that normal circular coaxial cable can be replaced with smaller cable having the same loss, hence having a weight and materials cost reduction over normal coax of about 40%.